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Jan
Under Reach And Overreach Of Relay. When θ is assumed 90 with variation of k between 02-05 relay is over- reached too. Overreaching distance relays tripping under load have played a part in many major blackouts. This overreaching applies to Z2 and Zpilot as well which is the reason that the reverse looking reaches will need to be extended to cover this scenario. If STATCOM is injecting the current into the system then the ratio is positive and it would lead to higher impedance to relay.
As a result the relay faces an underreach effect and fault location seems to be far away from the actual location. Overreaching distance relays tripping under load have played a part in many major blackouts. TT means that one relay is sending a Transfer Trip signal to the other. There should be a link on the screen right now that you can open in a new window if you want to follow along. The August 14 2003 blackout is the most notable recent event in North America demonstrating these tripping operations. Zone-2 is purposely set to detect faults in the section.
On other hand at θ 270 with changing k in the normal range of 02-05 per unit the relay becomes under-reached whereas for k 0 there is risk of under-reach.
The difference of 08 of the. This document describes the vulnerability of distance relays to overload tripping and discusses methods to minimize. Under-reach means that the relays effective reach fails to reach the setting value which might result in a failure to trip. A distance relay is said to under reach when the impedance seen by relay due to fault is more than the relay setting value even though the fault point is within the protected zone of line. Therefore at least one relay must measure a Zone-1 fault for this scheme to work. Fault inception angle changed from 0 to 180.